The present invention relates to a peel-apart instant film unit.
In peel-apart instant films (which are, hereinafter, referred to as film units for simplicity), two separate diffusion transfer sheets are used: a negative or photosensitive sheet in which a latent image is created as a result of exposure and a positive or image-receiving sheet where the positive image is formed. Sheets of negative and positive material are arranged separately in packs in such a way that the negative can be exposed, and then the two sheets can be pressed emulsion-to-emulsion when they are withdrawn from a camera or film holder. As the sheets emerge from the camera or film holder, they pass between two pressure-applying rollers which break a pod of viscous processing liquid or developer reagent and spread it uniformly between the two emulsions. When the two sheets are peeled away from each other upon the completion of processing a positive transfer image is formed in the image receiving sheet.
For this processing, the two sheets are interconnected to each other by means of a withdrawing sheet member and a mask member, and these sheets and members constitute a film unit as a whole.
The film unit is provided with a pod, mentioned above, which is ruptured to release the developer reagent contained therein when the film unit passes between the pressure rollers, and a flap connected to the trailing end of the negative sheet for forming trap means which receives excess developer reagent. In the film unit, there is also a funnel member for directing the released developer reagent from the ruptured pod between the two sheets.
In this type of peel-apart instant film unit, there is the disadvantage that it is impossible to observe the progress of the development of a positive image, since the two sheets are maintained superimposed emulsion-to-emulsion during processing. In this regard, the peel-apart instant film unit lacks the advantage of an integral type of instant film unit well known in the art in which the progress of development of a positive image is visible from the outside even during processing of the film unit. The fact that, in the peel-apart instant film, the developing positive image is invisible forces the user to peel apart the two sheets only after a period of time which is specifically indicated by the manufacturer of the film unit in order to ensure the completion of processing.
A film unit heretofore used has several disadvantages which make it difficult to implement the film unit in a practical environment. In particular, the conventional film unit may experience difficulties in forming the best positive image. In practice, because of the dependence of photographic processing on ambient temperatures, the film units are not able to provide the best positive images when they are subject to a predetermined processing period of time. For example, since photographic development proceeds slowly at fairly low ambient temperatures, the film unit is is insufficiently processed, resulting in a low quality of positive image. Conversely, specifying a processing time longer than that usually required, in consideration of the above problem, there will be a loss of time when the film unit is processed at an ambient temperature approximately equal to or higher than a normal processing temperature.